Summary/Abstract A recent review of trajectory research found that there is a great deal of research aimed at better understanding transitions in alcohol and other drug (AOD) use patterns from early to late adolescence and late adolescence to emerging adulthood. However, no studies to date have: a) 13 assessments of AOD use from age 10-24 across all developmental periods (middle school, high school, and emerging adulthood); b) a large sample with substantial racial and ethnic diversity, particularly among Hispanic and Asian youth; c) in-depth coverage of 10 areas of functioning across three key domains; d) subjective and objective neighborhood data; and e) the capacity to examine developmental trajectories for more than one substance. The current proposal continues R01AA016577 and R01AA020883 (PI: D?Amico), which together have assessed AOD use across nine waves of data from age 10 to age 19. The proposed study capitalizes on the longitudinal data on protective and risk factors we have collected since age 10 in a diverse cohort (44% Hispanic, 21% Asian, 21% white; 2% Black, 12% multiethnic/other; 54% female) by continuing to annually assess these youth in order to capture important transitions to emerging adulthood. Our specific aims are to: Aim 1a: Identify trajectories of alcohol, tobacco, marijuana, and other drug use from age 10 into emerging adulthood. Assess differences by race/ethnicity. Aim 1b: Examine individual (e.g., resistance self-efficacy), peer (e.g., peer use) and family (e.g., parent disapproval of use) factors that may impact these trajectories. Test for similarities/differences in these associations across racial/ethnic groups. Aim 2a: Merge the survey data with the largest existing database of neighborhood measures to examine effects of neighborhood characteristics (economic, social, demographic, alcohol and marijuana outlet density) on AOD trajectories. Aim 2b: Test for similarities/differences in these associations across racial/ethnic groups. Aim 3a: Examine how AOD use trajectories during middle and high school predict outcomes through age 24 in three core domains: 1) risk behaviors (e.g., AOD use, risky sexual behavior, delinquency), 2) health related quality of life (e.g., mental, physical, social), and 3) adult role functioning and transitions (e.g., education, relationships, life satisfaction). Aim 3b: Test for similarities/differences in these associations across racial/ethnic groups. Aim 4a: Using new data gathered annually from ages 20-24, examine how adult role functioning and transitions longitudinally predict subsequent changes in AOD use and other risk behaviors, as well as health-related quality of life, in emerging adulthood. Aim 4b: Test for similarities/differences in these associations across racial/ethnic groups. By advancing the epidemiology of alcohol use during adolescence and emerging adulthood, our findings can impact prevention and intervention programming for young people and address public health policy. 1